Hydrothermal synthesis of K, Na doped Cu-S nanocrystalline and effect of doping on crystal structure and performance

Abstract

Cuprous sulfide (Cu2S) nanocrystals and K or Na doped KCu7S4 nanowires and NaCu5S3 micro-nanospheres have been synthesized successfully by using a simple hydrothermal method, using KOH or NaOH as mineralizing agent, CuCl22H2O and S powders as copper and Sulfur sources, respectively. The structure and morphology are characterized and analyzed by X-ray diffraction (XRD), energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results reveal that under conditions that the amount of KOH is below 1g or the amount of NaOH below 2 g, the product is of the orthorhombic chalcocite Cu2S, while with high alkali amount (no less than 3 g), K+ or Na+ is successfully incorporated into the Cu-S structure; KCu7S4 has the pure tetragonal single crystal structure, and its uniform nanowires can be up to several tens of micrometers in length. Na doping has no effect on the morphology of the product, which forms the hexagonal NaCu5S3. The formation and growth of the product are closely related to the reaction temperature, reaction time and mineralizing agent. And, the formation and doping mechanisms are discussed. Finally, the influence of the alkali metal ion doping on the optical properties of the product is investigated. The diffuse reflectance spectra demonstrate that the optical band gaps of Cu2S, NaCu5S3 and KCu7S4 nanocrystallines is 1.21, 0.49, 0.42 eV, respectively. And K+ or Na+ doping greatly affects the optical characteristics.